ask the labs
Flats, Grooves, & Cracks
by Karlen McLean, ABOC, NCLC
BETTER FLATTER
Q Can you suggest frame adjustments for high-index lenses that will help visually sensitive patients adapt to a flatter base curve?
A Selecting a small frame cuts down on base curve adaptation problems. It also helps to select a small frame for extra thinness and also lighter weight.
Adding a little wrap to the frame can also help, but should be done as a last resort since some people don't like the look or feel of a wrap on their everyday eyewear.
Most common is someone who's used to a six-base and is now in a five or 4.75 base. Try to match the base curve as closely as possible to the base curve the patient is wearing.
— Shirley Alston, general manager, Precision Optical Laboratory, Inc., Gallaway, Tenn.
CHIP TIPS
Q Why are several of my grooved rimless lenses chipping? Sometimes it happens during mounting, and other times patients come in within a month with chips.
A Some frame companies have stopped making the nylon cord top liner on groove frames, and when brittle materials like plastic, mid-index, or glass are used, they often chip easier. Groove only tough materials such as poly and Trivex, or even 1.60 and 1.67.
Labs share the responsibility to make sure that their computer systems figure the correct thickness for grooving. Edgers need to be calibrated to place the groove where chipping is minimized.
When purchasing frames at the practice, take one of the sample lenses out of the frame and check for the nylon top liner. There are products on the market that provide a cushion for the lab to put over the metal top rim to prevent chipping. However, this won't fix the core problem. Taking a few seconds to evaluate the frame and lens material saves time and money and preserves patient trust in the practice.
— John Granby, president, Deschutes Optical, Bend, Ore.
| Cracking UP |
|---|
| Q I recently cracked a drilled rimless lens when cutting off the screw. And this isn't the first time it's happened. What am I doing wrong and how can I correct it? A We have two ways to avoid cracking the lenses when dealing with the screws on drilled rimless prescription lenses. The first is to cut the screw to the desired length before mounting the lenses. But the more successful way, is to use a Dremel tool with a cutting blade and slice the screw off at the nut after assembly. We suggest using polycarbonate or Trivex lenses only for drilled rimless mountings. — Robert Haney, rimless craftsman, |
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. E-mail: mcleank@lwwvisioncare.com. Fax: 215-643-1705. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebusiness.com.
![]({"src":"/media/mmgihfnn/82007.jpg","focalPoint":null,"crops":[{"alias":"thumbnail","width":1110,"height":700,"coordinates":null}]})